There may be no better way to learn about computers than to get your hands dirty and build your own. Wiring up the chips to one another and considering how the electrical signals flow between them is a great way to visualize how these components work together to make a digital computer. But modern computers are tremendously complex, and attempting to wire these components together on a breadboard or perfboard is completely futile. Save yourself the effort — it is never going to work.
For this reason, people that want to design and build their own computer generally work with parts from the early 1980s. These relatively simple chips most commonly use through-hole technology, which makes them easy to work with. And the low clock speeds of these systems make them suitable for use with breadboards and jumper wires. But truth be told, once you build a breadboard computer, there is typically little that you can actually do with it.
Consider Ben Eater’s very popular breadboard computer built around a 6502 processor. With just a few chips in the design, and only a character LCD to use for output, it is not especially capable. So lots of people put them away in their spare parts drawer soon after getting the “hello, world” code up and running. Dr. Matt Regan noticed that these computers actually do have a lot of potential, however. They just need a little bit of help.
Regan noted, for example, that Eater’s breadboard computer is not all that far away from the design of a Commodore VIC-20 computer, which can run all sorts of useful programs and games. But in order to convert the computer into a VIC-20, a custom VIC chip is required. This chip has long been out of production, and it is getting harder to come by with each passing year.
There are FPGA-based drop-in replacements available, but in the interests of education, Regan instead decided to replace the functionality of a VIC chip with a bunch of TTL logic chips and EPROMs that are still in production. Between that and the 65C02 CPU and support chips still being produced by Western Design Center, it would be possible to make a clone of the VIC-20 using all modern parts. And to make things a little bit nicer for those of us that don’t want to track down an old TV or conversion box, Regan also plans to modify the custom VIC such that it can output a VGA signal.
So far, the first video in the series has been released. These initial steps set the stage for the entire project by building a VIC-20-compatible circuit (minus the VIC replacement) on perfboard. But in the next video, Regan promises to have the computer output a VGA signal from the newly-designed VIC circuit. Since the VIC chip also handles sound output, that should be covered in a future video as well. If you want to play along at home, now is the time to wire up the core of your modern VIC-20. Check out the video for some help with getting started.
A VIC-20 clone with no VIC chip (📷: Dr. Matt Regan)
The core of the computer (📷: Dr. Matt Regan)
The VIC replacement circuit (📷: Dr. Matt Regan)
